Disk drives primarily store digital data in concentric tracks on the surface of a data storage disk and are commonly used for data storage in electronic devices. The data storage disk is typically a rotatable hard disk with a layer of magnetic material thereon, and data are read from or written to a desired track on the data storage disk using a read/write head that is held proximate to the track while the disk spins about its center at a constant angular velocity. To properly align the read/write head with a desired track during a read or write operation, disk drives generally use a closed-loop servo system that relies on servo data stored in servo sectors written on the disk surface when the disk drive is manufactured.
Some operations in a disk drive use a significant amount of energy, even when read or write commands are not being serviced by the disk drive. For example, continuously spinning the data storage disk requires approximately the same power whether or not read or write commands are being performed. Similarly, actively controlling read/write head position with the servo system involves performing servo sampling, signal processing, and associated decoding with a read channel, all of which utilize substantial computational resources, independent of read or write commands. Because disk drives are frequently used in portable electronic devices in which available power is limited, such as laptop computers, restricting such energy-intensive operations in a disk drive is generally desirable.